This invention relates to the electrical coupling of a touch-sensitive piezoelectric transducer to a voltage-responsive electric control circuit, and more particularly to a circuit for performing the coupling function in a reliable manner, despite the high impedance of the piezoelectric transducer output. The circuit is adapted for use with a keyless access system in which access to a locked area is obtained by the operation of a series of numbered or lettered buttons in a predetermined sequence.
A number of patents has been allowed for such access systems, among which is Haygood et al, U.S. Pat. No. 4,205,325 which discloses a sophisticated system wherein an operator selectively enters a five digit number into a keyboard on the door of a vehicle in order to gain access, open windows or trunk, etc. The keyboard has an individual switch for each key, and closure of the switch is achieved by pressing the associated key so that the operation is analagous to the selective depressing of a series of old fashioned push buttons.
Other patents relating to access systems are Ligman et al, U.S. Pat. No. 4,206,491 and Kompanek, U.S. Pat. No. 4,190,785. Patents relating to touch sensitive piezoelectric transducers and their manufacture are Kompanek U.S. Pat. No. 4,193,010 and Kompanek U.S. Pat. No. 4,056,654.